Photolithographically processable resists have recently been used broadly in semiconductor, MEMS and micromachine applications. In such applications, photolithographic processes can be achieved by carrying out patterning exposure on a substrate, and then developing with a developing liquid to thereby selectively remove exposure regions or non-exposure regions. Photolithographically processable resists (photoresists) come in a positive type and a negative type; and the positive type thereof is a type in which exposure portions are dissolved in a developing liquid, and the negative type thereof is a type in which the exposure portions reversely become insoluble. In electropackage applications and MEMS applications as advanced technologies, not only the forming capability of a uniform spin coating film but high aspect ratios, straight sidewall shapes in thick films, high adherence to substrates, and the like are demanded. The aspect ratio used here is an important property calculated from a resist film thickness/a pattern line width and indicating the performance of photolithography.
As such a photoresist, a negative chemically-amplified photoresist composition is known which is composed of a polyfunctional bisphenol A novolac epoxy resin (trade name: EPON SU-8 Resin, made by Resolution Performance Products LLC) and a photoacid generating agent (which is composed of a propylene carbonate solution of an aromatic sulfonium hexafluoroantimonate) such as CPI 6974 made by ACETO Corporate USA. The photoresist composition, because of having very low light absorption in the wavelength region of 350 to 450 nm, is known as a photoresist composition capable of being processed by thick-film photolithography. The photoresist composition is applied on various types of substrates by spin coating method, curtain coating method, or the like, thereafter baked to volatilize the solvent to thereby form a solid photoresist layer having a thickness of 100 μm or more, and further irradiated with near-ultraviolet light through a photomask by using one of various types of exposure methods such as contact exposure, proximity exposure, and projection exposure to be thereby subjected to a photolithographic processing. Then, the resultant is immersed in a developing liquid to thereby dissolve the non-exposure region, whereby high-resolution negative images of the photomask can be formed on the substrates.
On the other hand, in the fields of MEMS components, MEMS and semiconductor packages and the like, physical properties of package materials are known to affect the reliability of devices. MEMS devices and semiconductor devices are liable to be deteriorated in the properties by changes of the surrounding temperature and humidity and the influences by fine litters and dusts and to be damaged due to the subjection to mechanical vibrations and impacts. In order to protect MEMS and semiconductor devices from these external factors, the devices are provided for use in a form of being sealed with various types of materials, or in a form of being included in a cavity structure surrounded by an external wall of various types of materials, that is, as a package. In the cases of hermetic sealing methods using metals and ceramics as materials for sealants and external walls, although obtained packages are excellent in reliability, these have drawbacks of high production costs, poor dimensional accuracy and the like. By contrast, in the case of resin sealing using resins as materials for sealants and external walls, such a process has relatively low production costs and high dimensional accuracy, but has problems with moisture resistance, heat resistance and the like. For example, the exfoliation of a sealant from a substrate or a device by moisture absorbed from the external environment by a resin material, and the fault caused by outgases generated from a package in exposure to a high-temperature environment pose problems. When an adherend such as a glass or silicon substrate is joined on a cavity provided using a resin material, slight unevenness cannot be filled because the storage modulus of the resin is high, and there resultantly arises a problem such as generating voids in the interior of and on the outer periphery of the substrate. Further in recent years, due to the safety, the influence on human bodies, and the like, a resin material capable of being developed with an alkali and satisfying a high aspect ratio has been demanded.
Patent Literature 1 discloses that a photosensitive resin composition containing a polycarboxylic acid resin obtained by adding an alcoholic hydroxyl group-containing monocarboxylic acid compound to an epoxy group in an addition ratio of 50%, and further carboxylic acid-modifying the resultant with a polybasic acid anhydride is capable of being developed with an alkali. However, there is no description that an alkali-developing type photosensitive resin composition containing a polycarboxylic acid resin obtained by adding an alcoholic hydroxyl group-containing monocarboxylic acid compound to an epoxy group in an addition ratio of 80% or higher, and further carboxylic acid-modifying the resultant is excellent in sensitivity, alkali developability and resolution, and a cured product of the composition has a low storage modulus.
Patent Literature 2 discloses that an anionic electrodeposition coating composition excellent in coating stability can be obtained by adding as an additive an epoxy resin obtained by reacting an epoxy group with an aliphatic monocarboxylic acid or a carboxyl group-containing epoxy resin obtained by introducing a carboxyl group to part of hydroxyl groups of the epoxy resin; however, there is no mention of the alkali developability and joining property of the compositions.